<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style type="text/css">
			#parent{
				width:200px;height:200px;
				background: #f00;
				position: relative;
				margin-top:100px;
			}
			#child{
				border:20px solid transparent;
				border-bottom-color:#00f;
				position: absolute;
				left:80px;top:-40px;
			}
		</style>
	</head>
	<body>
		<div id="parent">
			<div id="child"></div>
		</div>
	</body>
</html>
